Spectroscopy is the science where a sample substance is analyzed by means of the spectra of light the sample absorbs or emits. Technological advancements in both wavelength-dispersive (WD-XRF) and energy-dispersive (ED-XRF) X-ray fluorescence instrumentation enable the spectroscopic analysis of virtually all types of sample materials. In this technology, sample cups or sample receptacles are employed to hold or contain liquid, solid and powdered specimens. Many conventional prior art sample cups consist of four components. The four components include a cell body with at least one open end; a thin film of material capable of covering the open end of the cell body; an annular collar used to pull the thin film of material taut over the open end of the cell body; and a snap-on ring used to secure the thin film of material in place. The thin film of material encloses a sample substance within the cell body and provides a sample surface plane which is exposed to an excitation source, such as an X-ray tube, during the spectrochemical analysis. Such conventional prior art cups are exemplified by U.S. Pat. No. Des. 238,693 entitled "CELL FOR X-RAY SPECTROSCOPY OR SIMILAR ARTICLE" issued on Feb. 3, 1976 to Monte J. Solazzi; U.S. Pat. No. 4,409,854 entitled "SAMPLE CUP WITH VENTING MEANS FOR USE IN X-RAY SPECTROSCOPY" issued on Oct. 18, 1983 to Michael C. Solazzi; U.S. Pat. No. 4,643,033 entitled "SAMPLE CUP FOR USE IN X-RAY SPECTROSCOPY" issued on Feb. 17, 1987 to Monte J. Solazzi; U.S. Pat. No. 4,665,759 entitled "SAMPLE CUP WITH A CANTILEVER BEAM VENTING MEANS" issued on May 19, 1987 to Monte J. Solazzi; and U.S. Pat. No. 4,698,210 entitled "SAMPLE CUP APPARATUS FOR USE IN X-RAY SPECTROSCOPY EMPLOYING SELECTIVELY OPERATED VENTING MEANS" issued on Oct. 6, 1987 to Michael C. Solazzi. All of the above patents are assigned to Chemplex Industries, the assignee herein.
During spectrochemical analysis it is essential for the surface of thin film material, which covers the opened top of the cell body, to remain planar in order to produce reliable dam. The area of the thin film material that covers the top of the cell body, is known as the sample surface plane. During the spectrochemical analysis of certain specimens that exhibit a high abrogation in air, the sample cup retaining the specimen may be placed within a vacuum or inert gas environment. Under conditions where pressure equalization is not implemented, the thin film of material covering the sample will distend or bow outwardly due to the differential in pressures between the area within the sample cup and the environment surrounding the sample cup. This places portions of the thin film of material closer to the source of excitation. This variation in distance from the sample plane to the source of excitation alters the intensity of the characteristic radiation of the specimen and also alters the intensity of radiation impinging upon the sample specimen from the excitation source. Consequently, the spectrochemical analysis may produce erroneous quantitative data. For applications in a gaseous environment where pressure is greater on the outside of the sample cup than within the sample cup, the thin film of material distends or is drawn into the hollow of the sample cup providing a concave sample surface. This effect increases the distance between the sample plane and the excitation source and results in erroneous analytical data.
In order to equalize pressure and eliminate distension of the sample surface plane, some sample cups are provided with a venting means. The venting means may be activated to provide pressure equalization between the inside and outside of the cup. Other sample cup designs include a main cell component with both ends opened. This double open-ended cup allows for attachment of the thin film sheet prior to the introduction of the sample. This design is useful for applications in an environment where continuous venting is desired from the moment of sample introduction.
In the prior art, when a sheet of the thin film material is positioned over the open end of a cell body by means of the annular collar, portions of the thin film of material extend beyond the collar along the outer walls of the cell body. This excess portion of the thin film of material has a tendency to flare away from the sides of the cell body and impairs the handling of the sample cup. As such, the excess thin film material must be trimmed from the sides of the cell body in order that the sample cup may be conveniently handled.
Furthermore, in the prior art, securing the thin film of material over the open end of the cell body is a two step process. First, the annular ring must be placed over the thin film of material so as to pull the thin film of material down along the sides of the cell body. Second, the snap-on ring must be applied to secure the thin film of material into place. The two step operation causes excessive manipulation of the thin film of material which often results in the ripping of the thin film of material as the thin film of material is repeatedly stressed against the cell body.
It is therefore an object of the present invention to provide an improved sample cup including a single piece snap-on collar designed to retain a thin film of material over the open end of a cell body, without having any portion of the thin film material extend beyond the snap-on collar. Such a design eliminates the need to trim extraneous thin film material from around the cell body. This simplifies sample cup preparation by reducing operational steps and labor required to assemble the sample cups.
It is also an object of the present invention to provide a sample cup which eliminates wrinkles in the thin film of material which covers the opened end of the cell body. The wrinkle-free thin film of material provides a consistently planar sample surface. Specially designed edges on the cell body prevent inadvertent tearing of the thin film sample support material during its attachment.